Influence of grazingland management on soil carbon

Lynch, D.H¹, Cohen, R. D.H.², Fredeen, A1., Patterson, G.³, and Martin, R.C¹.

SUMMARY

Agricultural soils, if properly managed, have the potential to act as a net sink for CO2, and contribute significantly to reducing greenhouse gas emissions. Soils maintained under grasslands store very large amounts of soil carbon and globally, grasslands account for 25% of all land surface stored C.

Native rangeland plants have co-evolved with rangeland animals, and it appears that vegetation is best maintained and the productivity of the native range is maximized under light grazing conditions (and fire). Limited published information exists on the potential for soil carbon gains through improved management of grazed grasslands of Canada.

A computer simulation (GrassGro model) of management-induced changes in range and pasture forage and livestock productivity was combined with spreadsheet analyses over a thirty year period to estimate the influence of improved grazing practices on soil carbon and farm profitability, across native rangelands and tame pastures of the southern Canadian Prairies..

Improved practices included complementary grazing (i.e., successively moving grazing cattle to forage of different grasses which mature at different times of the season) and reduced stocking density on rangeland; and N fertilization, seeded grass/legumes grazed continuously or rotationally, and reduced stocking density on tame pastures. The analysis included three ecoregions on the basis of similarities in climate and soil type. The study provided a first objective assessment of the potential changes in soil C storage, and the economic feasibility, of a range of potential improved practices for grazinglands of the Canadian Prairies.

Overall, The estimated potential combined soil organic C gain through improved management of Prairie grazinglands (11.5 Mha) was 0.465 MMT C yr-1 (or 1.63 MMT CO2 yr-1), slightly less than the 1.70 MMT CO2 yr-1 currently emitted from agricultural soils in Canada. Gains with N fertilization, however, were considered largely negated by associated energy (C) costs, N2O emissions, and shifts in grassland species. The study concluded that complementary grazing alone appears to offer the combined benefit of soil carbon gains while providing enhanced net returns to the producer.

¹ Department of Plant and Animal Sciences, Nova Scotia Agricultural College (NSAC), P.O. Box 550, Truro, Nova Scotia, Canada B2N-5E3
²Department of Animal and Poultry Science, University of Saskatchewan, Agriculture Bldg., 51 Campus Drive., Saskatoon, Saskatchewan, Canada; S7N 5A8
³Agriculture and Agri-Food Canada, Crop and Livestock Research Centre (Charlottetown), Engineering Building, 20 Tower Rd., P.O. Box 550, NSAC, Truro, Nova Scotia, Canada B2N 5E3

The full article is published in the Canadian Journal of Soil Science; Volume 85, Number 2, May 2005, pp 183-192